Surface computing devices have been developed which comprise a surface which is used both for displaying the graphical user interface and for user input. The surface computing devices detect the user's fingers on the surface or detect real, tangible objects which are manipulated by a user and this is referred to as a ‘tangible user interface’ (TUI). In an example, the objects may be gaming pieces which may be moved by a user and the motion can be detected by the surface computing device. The surface computing devices may be designed for use by a single user or they may be multi-user devices.
There are several techniques which have been developed for tracking or detecting objects on the surface, for example, using cameras to image objects from above the surface (a ‘top-down’ configuration) or using light sources to illuminate the surface from below and cameras to detect light reflected by objects in contact with the surface (a ‘bottom-up’ configuration). Another technique relies on frustrated total internal reflection (FTIR) to cause scattering of light when a fingertip is in contact with the surface, and this scattered light is detected by a camera below the surface.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known surface computing devices.